1. Field of the Invention
The present invention relates generally to refrigeration systems and more particularly to centrifugal compressor-expander unit to provide compression of low pressure vapor refrigerant for cooling cycle and expansion of high pressure vapor refrigerant for thermal power cycle. The unit has an electric drive motor with overhung shaft on both sides, a centrifugal compressor assembly is directly coupled and supported on one end of the drive shaft, and a centrifugal expander assembly is directly coupled and supported on the other end of the shaft. The main assembly of the motor, compressor and expander are contained in hermetically sealed enclosure or of semi-hermetic sealed compressor and expander assembly. In the present invention the expander provides part of the work required to drive the compressor, therefore, substantially improves the efficiency of the refrigeration cycle through reduction of the net work input into the system.
2. Description of the Prior Art
Vapor compression direct expansion refrigeration cycle is well known in the field of refrigeration/heatpump systems. In theoretical vapor compression refrigeration cycle, saturated vapor refrigerant at low pressure enters a compressor and undergoes isentropic compression. The high pressure vapor enters a condenser, where heat is rejected from the fluid at constant pressure, the working fluid leaves the condenser as saturated liquid, an adiabatic expansion process follows across a direct expansion valve or capillary tube. The working fluid is then absorbs heat and evaporates at constant pressure before entering the compressor.
In the past, the design of direct expansion refrigeration units has not generally taken advantage of the low temperature level energy rejected from the condenser. Generally only liquid expanders were employed to take advantage of energy lost in the execution of expansion through throttling of the liquid refrigerant. For example a refrigerant expander compressor system of this type was enclosed in U.S. Pat. No. 3,934,424, another example is an integral turbo compressor--expander system for refrigeration was used to permit power recovery by the compressor from the expansion of the liquid refrigerant is enclosed in U.S. Pat. No. 3,494,145.
Generally, however, systems as described above which utilize or attempt to utilize the work used in throttling or expansion process of liquid refrigerant fluids have not found wide acceptance. Accordingly, the equipment necessary for its recovery has not been thought to be economically feasible because very little work has been recovered and very small improvement of performance and efficiency of the basic vapor compression refrigeration cycle has been achieved.